Influence of ageing on high temperature tensile deformation of a Ni- based superalloy, HAYNES 282

Abstract

The effect of ageing time and temperature on the deformation mechanism and corresponding tensile properties are investigated in a gamma/gamma ' Ni-based superalloy, HAYNES 282. Through a systematic variation in duration (24 h and 216 h) and temperature of ageing (650 degrees C and 760 degrees C), a significant variation in strengthening microstructural features was achieved in the resulting microstructures. While in one case (650 degrees C, 24 h ageing condition), a microstructure with no gamma ' was observed, for the rest of the cases, gamma ' precipitates of varied sizes were observed. In one specific case (760 degrees C, 216 h ageing condition), very fine (4-6 nm) MC carbides were observed along with gamma ' precipitates; in which these tiny MC carbides became the deciding factor for strength over gamma ' precipitates. While common knowledge of smaller gamma ' precipitates giving higher strength could explain the higher strength at 760 degrees C, 24 h ageing condition as compared to 650 degrees C, 216 h ageing condition, the further increase in strength in case of 760 degrees C, 216 h ageing condition, even with much larger gamma ' precipitates was something quite interesting and counterintuitive. This paper elucidates this puzzling observation. The variation of tensile properties of these wide varieties of microstructures will be described in this paper in light of the underlying deformation mechanisms. A change in deformation mechanism from planar slip (microstructure with no gamma ') to twinning (microstructure with gamma ') and Orowan-looping (microstructure with gamma ' along with fine nano carbides) as a function of microstructure explains the difference in strength, ductility, and strain hardening phenomena among the varied ageing conditions.(c) 2022 Elsevier B.V. All rights reserved.